1. Field of the Invention
The present invention relates to a vibration wave driving apparatus and a manufacturing method of a vibration body therefor, and more particularly, to a vibration body serving as a constituent part of a linear ultrasonic motor and a manufacturing method of the vibration body.
2. Description of the Related Art
In the past, a vibration wave driving apparatus (linear ultrasonic motor) as described in Japanese Patent Application Laid-Open No. 2004-304887 has been suggested as a linear ultrasonic motor for linearly driving the driven body. Principle of driving such linear ultrasonic motor will be described with reference to FIGS. 7A to 7C. As shown in an external perspective view illustrating a linear ultrasonic motor in FIG. 7A, a linear ultrasonic motor 510 includes a vibrator 501, a slider 506, and a pressing member (not illustrated) for pressing the vibrator against the slider. The vibrator 501 includes an electro-mechanical energy conversion element 505, which is typically a piezoelectric element, and a vibration body that is bonded to one side of the electro-mechanical energy conversion element 505 so as to be integrated with the electro-mechanical energy conversion element 505. The vibration body includes a base portion 502, which is formed in a rectangular shape, and two projecting portions 503 and 504, which protrude from the upper surface of the base portion.
In an ultrasonic motor, a voltage having a specific frequency is applied to a piezoelectric element so as to excite a plurality of desired vibration modes, and these vibration modes are superimposed, thereby causing a driving vibration. In the case of the motor illustrated in FIG. 7A, two bending vibration modes are excited in the vibrator 501 illustrated in FIGS. 7B and 7C. Each of the two bending vibration modes is a bending vibration mode in an out-of-plane direction of the vibrator 501, which has a plate-like shape. One of the vibration modes is a second-order bending vibration mode (Mode-A) in the longitudinal direction of the vibrator 501, and the other of the vibration modes is a first-order bending vibration mode (Mode-B) in the width direction of the vibrator 501. The shape of the vibrator 501 is designed so that the resonant frequencies of the two vibration modes are the same or close to each other. The projecting portions 503 and 504 are each disposed in the vicinity of a node of the vibration in Mode-A. Due to the vibration in Mode-A, end surfaces 503-1 and 504-1 of the projecting portions each perform a pendulum motion around a pivot, which is a node of the vibration, and thereby perform a reciprocating motion in the X direction. The projecting portions 503 and 504 are each disposed in the vicinity of an antinode of the vibration in Mode-B. Due to the vibration in Mode-B, end surfaces 503-1 and 504-1 of the projecting portions each perform a reciprocating motion in the Z direction.
The vibrations in the two vibration modes (Mode-A and Mode-B) are excited simultaneously so that the phase difference between the two vibration modes is about ±π/2, and superimposed, whereby the end surfaces 503-1 and 504-1 of the projecting portions each perform an elliptical motion in the XZ plane. Due to the elliptical motions, the slider 506, which is in pressed into contact, can be driven in one direction. At this time, the projecting portions 503 and 504 of the vibrator 501 and the slider 506 intermittently come into contact with each other with the drive frequency of the vibrator 501 (which is several tens of kHz or higher). Therefore, appropriate contact is not achieved unless either of them have appropriate spring characteristics. The projecting portions 503 and 504 also function to amplify the vibration in the X direction as described above.
For the above reason, in order to fulfill these two functions, low-noise driving is realized by giving spring characteristics to the slider side when the configuration of the vibrator described in Japanese Patent Application Laid-Open No. 2004-304887 is made although this is not shown in Japanese Patent Application Laid-Open No. 2004-304887. On the other hand, Japanese Patent Application Laid-Open No. 2008-125147 suggests a vibration actuator in which spring characteristics are given to the projecting portions 503 and 504 and the projecting portions 503 and 504 are made into appropriate shapes as illustrated in FIGS. 8A to 8C, so that low-noise driving is realized.